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JOURNALS // Zapiski Nauchnykh Seminarov POMI // Archive

Zap. Nauchn. Sem. POMI, 2021 Volume 505, Pages 162–171 (Mi znsl7129)

Random section and random simplex inequality

A. E. Litvakab, D. N. Zaporozhetsc

a Dept. of Math. and Stat. Sciences, University of Alberta, Edmonton, AB, Canada, T6G 2G1
b Saint Petersburg State University
c St. Petersburg Department of Steklov Mathematical Institute of Russian Academy of Sciences

Abstract: Consider some convex body $K\subset\mathbb R^d$. Let $X_1,\dots, X_k$, where $k\leq d$, be random points independently and uniformly chosen in $K$, and let $\xi_k$ be a uniformly distributed random linear $k$-plane. We show that for $p\geq -d+k+1$,
$$ \mathbf E |K\cap\xi_k|^{d+p}\leq c_{d,k,p}\cdot|K|^k \mathbf E |\mathrm{conv}(0,X_1,\dots,X_k)|^p, $$
where $|\cdot|$ and $\mathrm{conv}$ denote the volume of correspondent dimension and the convex hull. The constant $c_{d,k,p}$ is such that for $k>1$ the equality holds if and only if $K$ is an ellipsoid centered at the origin, and for $k=1$ the inequality turns to equality.
If $p=0$, then the inequality reduces to the Busemann intersection inequality, and if $k=d$ – to the Busemann random simplex inequality.
We also present an affine version if this inequality which similarly generalizes the Schneider inequality and the Blaschke-Grömer inequality.

Key words and phrases: Blaschke-Grömer inequality, Blaschke-Petkantschin formula, Busemann intersection inequality, Busemann random simplex inequality, convex hull, expected volume, Furstenberg-Tzkoni formula, random section, Schneider inequality.

UDC: 519.2

Received: 11.11.2021



© Steklov Math. Inst. of RAS, 2025